Insulator



&

G. JANSSON INSULATOR Filed Feb; 23, 1926 Patented Aug. 4, 1931 UNITED STATES PATENT OFFICE .GUS'IAV J ANSSON, OF WOLLASTON, MASSACHUSETTS, ASSIGNOR TO CONDIT ELECTRICAL MANUFACTURING CORPORATION, PORATION OF MASSACHUSETTS OF SOUTH BOSTON, MASSACHUSETTS, A COR- INSULATOR Application filedl'ebruary 23, 1926. Serial No. 89,888.

This invention relates to insulators for high tension electrical apparatus wherein 1t is necessary to insulate closely related conducting members which are at widely different potentials, such as out-going and 1ncoming high tension leads for apparatusenclosed in metal casings; and more particularly to that type of insulator which consists of opposed insulating bodies hav ng an air space between them and disposed in the electrical field between the conducting members.

Diflerent dielectrics possess different powers of transmitting induction across them; hence the potential gradlentthrough any insulator composed of different insulating bodies depends upon the specific inductive capacity, or dielectric constant, of that body and is roughly inversely proportional to the specific inductive capacity. In an insulator composed of dissimilar nsulatn g bodies the potential gradient is different in each body and is greatest in that body hav ing the lowest specific inductive capacity. That insulating body having the greatest potential gradient through it is usually the one which is the most severely stressed and, consequently, is the most likely to fall. In aninsul'ator composed of opposed porcela n insulating bodies with an interposed air 'space,'as in certain bushing-type insulators, the potential "gradient in the air space is ordinarily much greater than that in the orcelain bodies, since porcelain has from Eve to six times the specific inductive capacity of air. The air layer in such an insula- .tor, therefore, is, the most liable to break down upon abnormal circuit disturbances.

It is an object of this-invention to provide an insulator of this general type which shall have an approximately uniform potential gradient throughout and which consequently will be more reliable in operation than previous insulators of this class.

A further object is generally to improve the construction and operation of high tension insulators.

Fig. 1 is an elevation, partly in section,

of an insulator suitableflior use in an eleccompartment 12, which space isapproximately co -extensive with the length of said tubes, and, preferably, has a relatively small cross-sectional dimension. A body of cement 13 is provided to unite the tubes rigidly together at their lower ends and also to form a bottom closure for the space 12. Grooves 14 in the tube walls at this point serve to increase the strength of the bond between the tubes and the cement.

An annular metal flange 15 is disposed about said outer tube 11 and is secured fixedly thereto by any suitable means, as a body of cement 15a and said flange serves as means to attach the insulator fixedly to the casing 15?) of any suitable electrical apparatus.

A metal bushing 16 may be received in the lower end of the axial passage 16a of the said inner tube 10 and secured fixedly in position in said tube by cement, or other r'su-i'table means. Said bushing may be provided with an outstanding annular flange 16?) which is adapted to bear against the lower end of said tube and receive any upward pressure'exerted against the bushing. conductor 17 is disposed within the axial passage 16a of said tube 10 and is screw-threaded at its 'lower end into the bushing 16 and is arranged to extend a substantial distan'ce below the bushing for connection with the apparatus within the easing by some suitable means.

A metal ferrule 19 is fixed to the upper :end of the outer tube 11 by a body of cement 20, or other suitable binding means, and extends over and provides a closure for the top-openings of both tubes 10 and 11. Said ferrule is also provided with the integral upstanding "flanged neck '21 which 'is'arranged to receive said conductor 1'? in its central opening 17a. A spline 22 is carried by said neck 21 and is provided to prevent the turning of the conductor within the neck 21, at the same time allowing for vertical movement between the conductor and the ferrule 19. To this end, said spline is received loosely in an axially-extended slot 22a in said conductor, which slot is suitably longer than said spline to permit free expansion and contraction of said conductor. A packing 23 of suitable insulating material may be interposed between the ferrule 19 and the top of the inner tube 10 to provide a yielding cushion against which said inner tube may expand.

The conductor 17 extends through and beyond the end of the ferrule 19 and is screw threaded into the metal terminal member 2a which comprises the threaded terminal stud 25 and the depending annular cup 26 which cup is arranged in covering relation with the conductorqaassage in the neck 21 and is free to slide thereon to provide for expansion and contraction of the conductor.

The structural features of the insulator above described and illustrated are not herein claimed but are described and claimed in my co-pending application Serial No. 89,889 filed February 23, 1926.

In the type of insulator above set forth, wherein the space 12 between the outer and inner tubes contains air, the potential gradio ent is exceedingly irregular, and may be approximately as illustrated by the line aa, Fig. 2. Since the specific inductive capacity of the air in the annular space 12 is much less than that of the porcelain of the tubes 10 and 11, the potential gradient in the air space is much greater than the potential gradient in the porcelain, as is indicated in an approximate manner, by that portion a of the gradient line lying in the air space. Such a nonuniform gradient line causes severe and concentrated local stresses to be set up, during abnormal circuit conditions, under which the insulator may fail.

In accordance with this invention I provide an insulator construction wherein the electric stresses are distributed in an approximately uniform manner through the insulating tubes and the air space, thereby improving the insulator as a whole, and eliminating localized portions under initially high stress. In carrying out my invention, I fill the air space 12 with a filler of loose granular insulating particles 18 of some suitable solid material which is characterized by having a specific inductive capacity greater than that of air. Preferably I employ porcelain since it is the material composing said tubes 10 and 11. I do not intend to limit myself to porcelain as I insulator.

may employ any material which has a high specific inductive capacity and providing that its use in said space 12 does not increase the specific inductive capacity of said space to a value where it greatly exceeds that of the tubes. Preferably the filler material is crushed or otherwise re duced to a granular form, and preferably relatively small granules, so that the proportion of material to voids between the granules is relatively high. The precise size of the granules cannot be stated; it will vary with the circumstances. The granular material may be introduced into the space 12 before the ferrule or cap 19 is cemented onto the top of the outer tube, although the precise method of introducing the filler material is not herein of importance. The granular filler material is adapted to exist in the space 12 in a loose, as contrasted with a compressed or solid. condition, although it may be compressed by its own weight or some packing, not shown, at the top of the Since the material composing, the filler has a greater specific inductivecapacity than that of air, the specific inductive capacity of the space 12 will be raised by that value, modified by the percentage of air voids between the granules. By suitably choosing the material, as by select ing one that has a specific inductive capacity sufiiciently greater than that of the material comprising the tubes 10 and 11, it is possible to bring the specific inductive capacity of the space 12 to equal that of said tubes. Such a condition is not essential, however, it being sufiicient if the space 12 and the tubes 10 and 11 are approximately the same within reasonable limits. The dotted line :11, Fig. 2, indicates approximately the potential gradient through the insulator when the space 12 is packed with a granular insulating material having a. specific induction capacity about equal to that of the porcelain composing said tubes 10 and 11. The line w is considerably more uniform, and less steep, than the line H, which consequently indicates that the localized high stresses in the insulator have been removed and that the ability of the insulator to resist abnormal potential conditions has been improved.

To further improve the insulator, I may fill the voids between the granules with a fluid insulating body, as oil, and so further enhance the specific inductive capacity of the space, oil having a higher specific inductive capacity than air although not so good in this respect as porcelain.

I claim:

1. In an insulator, the combination of two concentric insulating tubes having an annular space between them, and a loose granular filler of insulating material contained in said annular space.

2. In an insulator, the combination of two concentric insulating tubes, an annular space between said tubes, and a loose filler of granular material contained within said space, said filler-material having approximately the same electrical characteristics as those of the material composing the tubes.

3. In an insulator, the combination of outer and inner insulating tubes, a peripheral space between said tubes, and a loose filler of granular material similar to the material composing said tubes disposed within said space.

4. The combination of two opposed and spaced insulating bodies the remote faces of which are adapted to be subjected to different potentials and a loose filler of granular insulating material contained in the space between said insulating bodies the specific inductive capacity of the material of said filler being such that the potential gradient through said space is approximately the same as that through said insulating bodies.

5. In an insulator, the combination of two concentric insulating tubes having an annular space between them, a loose filler of granular insulating material contained within said space, and a fluid insulator arranged to fill the voids between said granular material, said fluid having a dielectric constant greater than that of air. I

6. In an insulator, the combination of concentric insulating tubes having an annular space between them, and a loose filler of granular material disposed within said space, said filler comprising a material having a dielectric constant which at least is not materially lower than that of the material of said tubes whereby the dielectric constant of the insulation between said tubes is not materially lower than that of the tubes. 1

7 An electric insulating bushing comprising a pair of closely spaced solid insulating bodies, and a body of granular insulating particles and an insulating fluid distributed uniformly as a filler in the space between said bodies, the material of said granular insulating particles characterized by having a specific inductive capacity which at least is not materially lower than that of the material composing said insulating bodies, and the size of the granular particles being such as to regulate the proportionate amounts of granular particles and insulating fluid in the space to provide a resultant speciflc inductive capacity of the filled space between said bodies which is substantially equal to that of the material composing said insulating bodies.

In testimony whereof, I have signed my name to this specification.

GUSTAV J ANSSON. 

